textproduct: Albany

WHAT HAS CHANGED

Marginal Risk (Level 1 of 5) for severe thunderstorms south and west of Albany for Wed-Wed Night.

Cooler max temps were continued from the Capital Region and Berkshires north and east today and Wed. Also the greater threat for moderate to locally heavy rainfall continues to be Wed night/Thu morning with the strong short-wave and the occluded front.

KEY MESSAGES

1) Low pressure system and approaching warm front bring showers and non-severe thunderstorms this morning with locally heavy rainfall.

2) A few strong to severe thunderstorms possible south and west of the Capital Region this afternoon into this evening with an isolated flash flood threat for the region.

3) Additional rounds of showers and thunderstorms late Wednesday afternoon into Thursday with some strong/severe thunderstorms (Wed-Wed night) and isolated to scattered instances of heavy rainfall/flash flooding possible.

DISCUSSION

KEY MESSAGE 1...

High pressure is near southeast New England this morning with a stationary front over the eastern Great Lakes Region, western NY and and w-central PA. The mid and upper-level flow will be west to northwest with ridging over the Upper Midwest, northern Great Lakes Region and Ontario. A mid and upper level short-wave and the frontal boundary lifting slightly north and east in the mid to late morning will focus showers with some embedded thunderstorms. Mean MUCAPE values on the latest HREF are generally under 300 J/kg with negative Showalter stability indices indicative of some elevated instability today. The low pressure system or weakening MCS on some of the CAMS is supported by the right entrance region of a mid and upper level jet streak which will enhanced the lift and pcpn. PWATs will be in the 1.50-2.0" range from north to south across the region which are 1-2.5" STDEVS above normal according to HREFs.

Based on several of the CAMs, the heaviest rainfall looks like it will fall from the Mohawk Valley, Greater Capital Region and the Berkshires northward. Hourly rainfall rates based on the latest HREF could briefly be in the 0.25-0.50" range with some locally higher amounts up to an inch/hr. The rainfall should diminish by the late morning/early evening with an outflow boundary drifting southward which may focus a severe threat for the later afternoon. An isolated flash flood (WPC Day 1 ERO Level 1 of 4) threat exists with any enhanced rainfall rates, though gridded 1-hr/3-hr FFG values remain high. At the very least, ponding of water on roadways/low-lying areas for the morning commute and/or poor drainage flooding of urban areas will be possible. Plenty of clouds and spotty light rain will linger into the afternoon, especially north of the mid Hudson Valley and eastern Catskills.

KEY MESSAGE 2...

The warm front stalls and actually retreats back to the south/southwest in the late afternoon/evening. It is possible on the warm side of the boundary that some strong to potentially severe thunderstorms develop. The focus will be an outflow boundary from the morning system and the front. The latest HREFs still show mean SBCAPEs of 750-1500 J/kg with 0-6 km deep shear 40-45 KT along the west/southwest border of the WFO ALY forecast area across the northern/eastern Catskills, mid Hudson Valley, southern Taconics and NW CT. SPC maintains a Marginal Risk (Level 1 of 5) for most this region with a Slight Risk (Level 2 of 5) for Ulster and Dutchess Counties close to I-84. A gradient of instability exists and overlaps with shear with a potential outflow boundary. Some of the CAMs show the potential for some organized deep convection with an isolated super cell threat with damaging winds and large hail the main hazards. However, with a boundary and some backed low-level flow with enhanced 0-1 km helicity/shear and potential low LCL heights, an isolated tornado can not be ruled out in the mid Hudson Valley or close to the I-84 corridor. If it remains cloudy, then severe/strong thunderstorm threat will diminish late this pm and into tonight. Max temps will run cool from the I-90 corridor north and east with the east to northeast low-level flow and we blended with MAV MOS with the NBM for highs in the mid 60s to lower 70s in these areas with some mid 70s to around 80F southward.

KEY MESSAGE 3...

Much of Tue night into early Wed will be mostly cloudy with some patchy light rain showers/drizzle with patchy fog due to the 1025 hPa or sfc high keeping the frontal boundary south and west of the region. However, a strong mid/upper level short-wave and an occluded front approaches from the west Wed pm. The timing for any strong to severe thunderstorms looks to be in the late pm into the early evening. On some of the CAMs, an MCS forms over southeast Ontario and the eastern Great Lakes in the mid to late pm and races towards the western Dacks/western Mohawk. MUCAPES rise to 1000-1500 J/kg west of the Hudson River Valley with MLCAPES in 750 J/kg or less. The deep shear remains 40-50 KT. SPC introduced in the latest Day 2 Outlook a Marginal Risk (Level 1 of 5) for locations west and southwest of Albany. Isolated instances of damaging winds and large hail would be the main threats. The limited instability along and east of the Hudson River Valley should limit the severe threat.

The heavy rainfall threat still exists Wed night into Thu morning, PWATs remain 1 to 2 STDEVS above normal in the 1.5-2.0" range on the various CAMs. The strongly forced wave could produce some training/back building convection especially from the Schoharie Valley and the Capital Region north and west. Hourly rainfall rates 1" or more an hour could occur. WPC maintains a Slight Risk (Level 2 of 4) for scattered instances of flash flooding possible from the Schoharie Valley/Capital Region north and west with a Marginal Risk (Level 1 of 4) south and east of these areas. A Marginal Risk continues south and east of the southern Dacks and Lake George south and east for after 12Z Thu (WPC Day 3 ERO). We have to see where the rainfall is heaviest today and evaluate where soils may be more saturated. A short-fuse Flood Watch for potential isolated to scattered flash flood instances may be needed in the future for Wed night into Thu. The main stem rivers are not projected to flood, but poor drainage flooding of urban areas, small creek and stream flooding may be possible where any training occurs. The threat for isolated to scattered thunderstorms continues on Thu with the front moving southward. Latest NBM 24-hr probabilities >1" rainfall for the period ending 8 pm Thu are 50-80% and >2" for the same time frame are 20-45% across the forecast area. The highest probabilities are in the w-central Mohawk Valley and the southwest Adirondacks. Total rainfall from the MCS/occluded front could range from 1-2" over the northern half of the hydro service area with some localized higher amounts up to 3"

A cooler, drier and less humid air mass builds in Friday with seasonable/slightly below temps for the holiday weekend with next chance of a shower possibly on Labor Day.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Ceilings continue to fluctuate between MVFR and IFR conditions for all TAF sites at the start of this TAF period. IFR conditions should persist through the TAF period due to passing rain showers lowering visibility and low cloud ceilings as a weather system moves through today. Confidence continues to be low for thunderstorm potential this afternoon across TAF sites, so continued mention in PROB30 groups from 18z to 22z at KALB, KGFL, and KPOU and 18z to 02/00z for KPSF. Winds continue range between calm to light and variable through the TAF period.

Outlook...

Wednesday Night: High Operational Impact. Definite SHRA...TSRA. Thursday: High Operational Impact. Likely SHRA...TSRA. Thursday Night: No Operational Impact. NO SIG WX. Friday: No Operational Impact. NO SIG WX. Friday Night: No Operational Impact. NO SIG WX. Saturday: No Operational Impact. NO SIG WX.

ALY WATCHES/WARNINGS/ADVISORIES

CT...None. NY...None. MA...None. VT...None.